Unzip both files in plugin directory of VIM, modify "selfreqfiles.txt" to meet your need. PRJ1/PRJ2 is menu selection will pop up when F1 or Sft-F1 pressed on key board, Default file name will be opened in respective directory upon selection so dont forget to modify it according to your need,
(This is first version it does not like if there is more then one space between names)

PRJ1 c:\PRJ1DIR1 DEFFILEPRJ1.C
PRJ2 c:\PRJ1DIR2 DEFFILEPRJ2.C

install details

Unzip and drop them in plugin directory and modify "selfreqfiles.txt" according to your most active projects. It saves time when going between projects when working on multiple projects and dont have time to tweak hotkeys.